To address increasing performance demand in mobile networks, a solution referred to as heterogeneous network deployment may be used to provide an enhanced higher data rate for a given user equipment (UE) and/or to increase the network capacity, e.g., in terms of UEs which may be served in a given coverage region. In such heterogeneous network deployment, it is possible to supplement the coverage region of a base station by one or more further base stations. Such further base stations are also referred to as pico base stations. The pico base stations may be low power nodes with a reduced spatial coverage as compared to primary base stations used for providing basic coverage. In a heterogeneous network deployment such primary radio station is also referred to as macro station. In a heterogeneous network deployment, the cells of the mobile network may be organized in a hierarchical manner: One or more pico cells, each served by a corresponding pico base station, may be located within the coverage region of a macro cell, served by the macro cell. In view of this hierarchical structure, the pico cell(s) may be regarded as subordinate cells, and the macro cell may be regarded as a superordinate cell.
However, usage of additional base stations generally increases energy consumption of the network. Also, the enhancements provided by the additional base stations may not be needed at all times. For example, the traffic load may vary according to a certain pattern: In the business hours the traffic load may be high and during the night the traffic load may be low. In view of energy consumption, it may therefore be beneficial to deactivate pico cells at certain times. Such deactivation may also be performed dynamically, depending on the traffic load.
For example, WO 2011/083947 A1 describes a solution in which a subordinate cell is activated when the traffic load in the superordinate cell exceeds a threshold. The selection of the subordinate cell to activate is based on measurements of downlink channel quality reported by UEs. In this case, the base stations of the subordinate cells need to temporarily transmit downlink signals to allow for the measurement of the downlink channel quality. This may cause frequent switching between modes of these base stations, which may in turn reduce their lifetime. Further, the temporary activation of downlink transmission by these base stations may cause unnecessary power consumption. Moreover, the temporary activation of downlink transmission may cause unnecessary interference. Still further, the measurement reports from the UEs increase the signaling overhead on the uplink radio channel and may require adaptation of control protocols on the radio interface.
Accordingly, there is a need for techniques which allow for efficiently controlling cell activity of subordinate cells in a mobile network.